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SiCp / Mg-Al 복합재료의 조직에 미치는 용융가공의 영향
윤여창,최정철,남태운,박익민 ( Yeo Chang Yoon,Jeong Cheol Choi,Tae Woon Nam,Ik Min Park ) 한국주조공학회 1993 한국주조공학회지 Vol.13 No.4
N/A Mg-9wt.%Al and Mg-9wt.%-1.6wt%Zn/SiCp(particle size 40㎛) metal-matrix-composite specimens were manufactured by rheo-compocasting method, known for its effect of improving the wettability. The ceramic reinforcement particles(SiCp) were dispersed in the semi-solid magnesium alloy matrix slurry being vigorously stirred in a high frequency induction furnace under inert atmosphere. A microstructural study of the dispersed particles in the specimens, prepared under different conditions as regards the time(10min, 20min, 30min) and temperature of the stirring, was made with the aid of optical microscope and SEM. The effect of superheating was also observed. It is revealed that 30 minutes` stirring time of the semi-solid at 40% solid fraction temperature(Mg-9wt.%Al : 590℃, AZ91 : 576℃), as determined by the lever rule, gives a satisfactorily uniform distribution of the particles. The superheating is observed to enhance further the uniformity.
Diamond Wheel 용 Cu-Sn 기지의 유리연삭에 미치는 특성에 관한 연구
최성국,서형석,최정철 ( Sung Kook Choi,Hyung Suck Suh,Jeong Cheol Choe ) 한국주조공학회 1992 한국주조공학회지 Vol.12 No.4
N/A Diamond is the hardest material known to humans, also possesses the highest thermal conductivity and a very low thermal expansion coefficient. Therefore, these properties of diamond make them logical choices for many difficult grinding application. Bonding material is a very important factor to performance of a grinding wheel. Grinding glass constitutes one of the major application areas of diamond grinding wheels, and Cu-Sn tin bronze matrix is widely used as a metal bond of diamond wheel in grinding glass but these studies are rarely reported. The bronze test pieces excluding diamond are sintered by the method of hot sizing respectively at 600℃, 650℃, 700℃, with a composition(Cu-10wt%Sn) on a phase and two compositions(Cu-20wt%Sn and Cu-23wt%Sn) on α+β phase. The rupture strength of Cu-10wt%Sn is highest. The bronze bonded diamond wheels are manufactured by same conditions as the bronze test pieces. The results of grinding ratio of wheels are highest in case of Cu-10wt%Sn bonded wheel sintered at 650℃ and grinding power is highest in same composition sintered at 700℃.
Cu-Sn(P) 합금의 용질재분배에 (溶質再分配) 관한 연구
서수정,조순형,김익수,윤의박,최정철 ( Su Jeong Shur,Soon Hyung Cho,Ik Soo Kim,Eui Pak Yoon,Jeong Cheol Choi ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.3
N/A In this, we have investigated the solute behavior in front of solid-liquid interface according to the change of the cooling rate in bronze alloy and phosphor bronze alloy. The conclusive summary is as follows: 1) The secondary dendrite arm spacing was decreased with increasing the cooling rate. 2) The minimum solute concentration happened to along centerline of primary arm, and the maximum solute concentration was found at the boundary of arm or between the arms the minimum solute concentration was increased with the cooling rate. 3) Segregation Index S was decreased with increasing the cooling rate and content of P. 4) The degree of the microsegregation was decreased with increasing the cooling rate. The effective distribution coefficient, Ke was increased with addition of P in Cu-Sn.
진행된 두경부암 환자에서 혈청 SCC 항원, CA 19-9, CA 125, DNA Microsatellite 변이와 재발 여부와의 관계
최종욱(Jong Ouck Choi),최정철(Jeong Cheol Choi),주형로(Hyung Ro Chu) 대한두경부종양학회 2001 대한두경부 종양학회지 Vol.17 No.2
Objectives: This study was designed to investigate the significance of serum SCC antigen, CA 19-9, CA 125 level and DNA microsatellite alterations (MSA) as prognostic factors and indicators for recurrences in the pre-treatment and post-treatment state, respectively in head and neck cancer patients. Materials and Methods: 120 patients who received curative treatment for head and neck cancer from 1995 to 2000 were followed up successfully, and were analyzed retrospectively. Thirty healthy subjects served as normal controls. Serum SCC Ag levels were measured by microparticle enzyme immunoassay technique via IMX SCC assay, CA 19-9 levels were measured by CA 19-9 RIA test kit, and CA 125 levels were measured by CA 125 IRMA kit. MSA were identified after PCR amplification. Heterozygosity was considered lost if the ratio of one allele was significantly decreased (>50%) in serum DNA compared with normal DNA from lymphocytes. Results: Preoperative tumor markers were higher in cancer patients than control, but not significant. Postoperative SCC Ag levels were lower than preoperative levels. The SCC Ag levels were remained low in no evidence of disease (NED) group, but increased in locoregional recurrence and distant metastasis group. CA 19-9 and CA 125 levels showed no correlation between levels and recurrences and were not decreased significantly after primary tumor removal. MSA were detected in five out of 21 cases, and highly detected in distant metastasis group. Conclusion: SCC Ag seems to be a helpful serum tumor marker for early detection of recurrence and distant metastasis of head and neck cancer after curative treatment. But, CA 19-9 and CA 125 were not reliable markers for head and neck tumors. MSA were not statistically significant because of the small number of study group. However they may be helpful for screening serum molecular markers for early detection of distant metastasis of head and neck cancers.